Web transport systems are used in a variety of applications to transport a web from one location to another. In printing applications, a printing assembly including one or multiple print heads positioned near the web prints patterns onto the web. As the ink is ejected on to the web, the web must remain flat and a predictable distance away from the printing assembly. Web unevenness or variations in distance from the printing assembly can result in poor printing quality.
To ensure web flatness, one solution often implemented in the prior art is to stretch the web between two rollers. The distance between the rollers affects the flatness of the web. For example, if the two rollers are placed a long distance from each other the web can unpredictably flutter up and down. To prevent this fluttering action more rollers can be added to the web path to reduce the distance between adjacent rollers and the rollers are positioned to provide an arcuate path for the web. Both the addition of the rollers and the arcuate positioning of the rollers are required to reduce the fluttering action.
FIG. 9 shows a prior art implementation of a web transport system with a series of printing print heads. In order to implement an extended web printing station 10, rollers 20 are provided for print heads 30. The required flatness of the web 40 is maintained by placing a roller 20 under each print head 30 and positioning the rollers to provide an arc. By placing the rollers in an arcuate path, as shown in FIG. 9, the web 40 is ensured to maintain contact with each roller 20. For example, three degrees of contact between each roller and the web may be achieved by the arcuate path shown in FIG. 9.
One challenge with the web transport system of FIG. 9 is that the arcuate path requires print heads to be positioned at different angles. The angular placement of the print heads is necessary to enable the print heads to be perpendicular to the surface of the web. If the print heads are angularly oriented with respect to the web surface poor quality printing may result.
In the web transport system of FIG. 9, a one-to-one correspondence exists between the rollers and the number of print heads. As the number of print heads increases in longer printing systems, so does the number of rollers. Because each roller makes sliding contact with the web, the rollers can dislodge dust and other particulate matter from the web. This particulate matter may affect print quality, require more frequent system cleaning, or necessitate ventilation and removal of the dust from the system.